Walk-behind self-propelled working machines having two different drive sources are well known in the art and disclosed in, for example, Japanese Patent Laid-Open Publication No. 2001-161104.
FIG. 9 hereof shows, in side elevation, the walk-behind self-propelled working machine disclosed in the above publication.
The working machine designated generally at 200 includes a machine body 201, an engine 202 mounted on the body 201, a generator 205 having a drive shaft, an electric motor 206, traveling wheels 203, and a rotary working member 207. The engine 202 has an output shaft operatively connected to the wheels 203 to rotate the same for propelling the machine 200. The output shaft of the engine is also operatively connected to the drive shaft of the generator 205 for driving the generator 205. The generator 205 then generates and supplies an electric power to the electric motor 206. The electric motor 206 thus supplied with the electric power drives the working member 207 for performing a work. The working machine 200 can thus travel while performing the work.
Known engines for walk-behind working machines of the same type as the above have a cylinder disposed vertically and upward, and a crankshaft disposed horizontally. The crankshaft projects from an engine body in a rearward direction of the machine body. The crankshaft has a driving pulley mounted thereon. Known generators used with the engine have a drive shaft having a driven pulley mounted thereon. The driving pulley and driven pulley are connected by a drive belt.
When the engine is driven to rotate the crankshaft, the driving pulley is rotated by the rotating crankshaft. The rotation of the driving pulley causes the drive belt to rotate the driven pulley. The driven pulley then rotates the drive shaft of the generator for driving the generator.
For transmission of rotation of the crankshaft of the engine to the drive shaft of the generator through the drive belt, the drive shaft of the generator is preferably disposed in parallel to the crankshaft of the engine. For this reason, the generator is usually disposed in a horizontal position.
The generator is required to generate a large amount of electric power for driving an electric motor to drive a rotary working member. Thus, the generator generates a large amount of heat.
To release the large amount of heat generated from the generator with high efficiency, it is preferred that the generator be arranged in the same direction as the flow of air surrounding the generator. However, the horizontal disposition of the generator is difficult to achieve the highly efficient releasing of the large amount of heat generated by the generator.
The crankshaft extends horizontally and rearward of the machine body, and is positioned above the bottom of the engine. The generator is also positioned above the bottom of the engine with the drive shaft disposed in parallel to the crankshaft. Because the generator is disposed above the bottom of the engine, the center of gravity of the working machine is undesirably positioned less low.
The generator is positioned rearward of the engine. Thus, the overall length of the working machine having the thus arranged generator is undesirably larger. The working machine of such a large overall length is not rendered compact.